U.S. Pat. No. 4,747,801, and the corresponding French published patent application No. 2 593 252A, describe a torsion damping device of the general kind defined above, and to which the present invention is particularly directed. In that arrangement, in order to provide a circumferential clearance on either side of the arms forming part of one of the coaxial parts, in the unstressed state of the assembly, centering means are associated with at least one of those arms. The, or each, centering means comprise a spacer member extending circumferentially between two successive ones of the through openings which accommodate the resilient members (known as the "main" resilient members), and, acting between this spacer member and the associated arm, a resilient centering member having a stiffness which is relatively low compared with that of the main resilient members.
In the above mentioned United States patent, the main resilient members bear circumferentially at their ends on insert members, and the circumferential spacer member extends integrally from one of these insert members to the other. In addition, the arm concerned carries pivot fingers which extend circumferentially for engagement with the insert members, which are formed with cavities to receive the pivot fingers for this purpose. The circumferential spacer member extends along the same circumference as these pivot fingers. It thus extends from the bottom of the cavity of one of the insert members to the bottom of the cavity in the other. As a result, it is necessary to move the insert members away from each other in order to insert the spacer member in place, and this also entails moving the main resilient members, bearing on the insert members, further apart. Given that these main resilient members are relatively stiff, the assembly operation is thereby made somewhat difficult.